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Thursday, September 8, 2011

Earthquake Royal Commission - The Performance of Unreinforced Masonry Buildings in the 2010-2011 Canterbury Earthquake Swarm

From the Royal Commission's website:

The Commission sought the advice of Associate Professor Jason Ingham from Auckland University and Professor Michael Griffith from Adelaide University on the Performance of Unreinforced Masonry Buildings in the 2010-2011 Canterbury Earthquake Swarm. Unreinforced masonry is defined as a construction of clay brick, concrete blocks or natural stone units bound together using lime or cement mortar, without any reinforcing elements such as steel reinforcing bars.

The report discusses the architectural characteristics and seismic vulnerability of unreinforced masonry buildings in New Zealand, makes observations about the performance of such buildings in the Canterbury earthquakes and available techniques for seismic upgrading. Section 7 recommends certain structural elements of all unreinforced masonry buildings be improved to meet the standard for new buildings and that other elements be improved to meet at least 67% of the standard required for new buildings. The authors also recommend that there be one national standard instead of policies being set by individual territorial authorities.

The report is large and has been divided up into small parts for ease of reference and downloading. All parts of the report can be downloaded fromhere.

The executive summary provides the main recommendations of the report:

All URM buildings should be improved so that the public is protected from all falling hazards such as chimneys, parapets, gable end walls and out-of-plane wall failures. These parts of URM buildings should be improved to the full design strength required for new buildings in New Zealand. If required, further building improvements should aim for 100% of the requirements for new buildings with lower values negotiable on a case by case basis. However, a minimum of 67% is recommended.

There should be a single, national policy for URM building maintenance and seismic strengthening rather than multiple regional policies.

The estimated cost to upgrade all of New Zealand’s approximately 3867 URM buildings to a minimum of 67% of the NBS requirements is approximately $2 billion. This is slightly more than the estimated value of $1.5 billion for the total URM building stock. Clearly, a cost effective strategy is needed to direct the limited resources available to tackle this problem.

Field testing of a limited number of existing URM buildings in the Christchurch CBD or nearby (that have been listed for demolition) would improve the current understanding of the seismic capacity of these buildings as well as offer an opportunity to develop and validate more cost-effective seismic strengthening/retrofit technologies. Such testing would focus on global structural performance characteristics and how loads are transmitted through buildings, and would be undertaken using such techniques as snap back testing to generate lateral loads and deformations that simulate earthquake effects. The performance of structural elements either extracted from such buildings, or tested in place, would also provide important new information.

In view of the estimated cost to upgrade all URM buildings to a minimum of 67% of the NBS, it is proposed that first priority be given to ensuring public safety by securing/removing falling hazards as outlined in section 7: Recommendation 3, Stage 1 and Stage 2. The cost to do this is unknown but would be substantially less than the amount to fully upgrade all buildings.

The report consists of:

ACKNOWLEDGEMENTS

TABLE OF CONTENTS

GLOSSARY AND ABBREVIATIONS

EXECUTIVE SUMMARY

SECTION 1: INTRODUCTION AND BACKGROUND

1.1 SCOPE AND PURPOSE
1.2 EUROPEAN SETTLEMENT OF CHRISTCHURCH
1.3 THE EVOLUTION OF NEW ZEALAND BUILDING CODES
1.4 BRIEF COMMENTS ON THE SEISMOLOGICAL CHARACTERISTICS OF THE 2010/2011 CANTERBURY EARTHQUAKE SWARM

SECTION 2: THE ARCHITECTURAL CHARACTERISTICS AND THE NUMBER AND SEISMIC VULNERABILITY OF UNREINFORCED MASONRY BUILDINGS IN NEW ZEALAND

2.1 EARLY MASONRY CONSTRUCTION IN NEW ZEALAND
2.2 ARCHITECTURAL CHARACTERISATION OF NEW ZEALAND’S URM BUILDING STOCK
2.3 NEW ZEALAND URM BUILDING POPULATION AND DISTRIBUTION
2.4 VALUE OF THE NEW ZEALAND URM BUILDING STOCK
2.5 SEISMIC VULNERABILITY OF THE NEW ZEALAND URM BUILDING STOCK

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